Cobalt-molybdenum sulfide catalyst materials and methods for stable alcohol production from syngas

ABSTRACT

The present invention provides methods and compositions for the chemical conversion of syngas to alcohols. The invention includes catalyst compositions, methods of making the catalysts, and methods of using the catalysts including techniques to maintain catalyst stability. Certain embodiments teach compositions for catalyzing the conversion of syngas into products comprising at least one C 1 -C 4  alcohol, such as ethanol. These compositions generally include cobalt, molybdenum, and sulfur, and avoid metal carbides both initially and during reactor operation.

PRIORITY DATA

This patent application is a continuation-in-part of U.S. patentapplication Ser. No. 12/204,543 for “COBALT-MOLYBDENUM SULFIDE CATALYSTMATERIALS AND METHODS FOR ETHANOL PRODUCTION FROM SYNGAS,” filed Sep. 4,2008. This patent application also claims priority to U.S. ProvisionalPatent Application No. 61/174,528 for “COBALT-MOLYBDENUM SULFIDECATALYST MATERIALS AND METHODS FOR STABLE ALCOHOL PRODUCTION FROMSYNGAS,” filed May 1, 2009. Each of these patent applications isincorporated by reference herein for all purposes.

FIELD OF THE INVENTION

The present invention generally relates to the field of catalysts forthe chemical conversion of synthesis gas to alcohols. The inventionrelates to catalyst compositions, methods of making catalysts, methodsof using catalysts, methods of maintaining catalytic activity, andmethods of characterizing catalysts.

BACKGROUND OF THE INVENTION

Synthesis gas (hereinafter referred to as syngas) is a mixture ofhydrogen (H₂) and carbon monoxide (CO). Syngas can be produced, inprinciple, from virtually any feedstock material containing carbon.Carbonaceous materials commonly include fossil resources such as naturalgas, petroleum, coal, and lignite. Renewable resources such aslignocellulosic biomass and various carbon-rich waste materials can alsobe used to produce syngas. It is preferable to utilize a renewableresource to produce syngas because of the rising economic,environmental, and social costs associated with fossil resources.

There exist a variety of conversion technologies to turn these variousfeedstocks into syngas. Conversion approaches can utilize a combinationof one or more steps comprising gasification, pyrolysis, steamreforming, and/or partial oxidation of a carbon-containing feedstock.

Syngas is a platform intermediate in the chemical and biorefiningindustries and has a vast number of uses. Syngas can be converted intoalkanes, olefins, oxygenates, and alcohols. These chemicals can beblended into, or used directly as, diesel fuel, gasoline, and otherliquid fuels. Syngas can also be directly combusted to produce heat andpower.

U.S. Pat. No. 4,752,623 (Stevens and Conway) discloses a catalyst forproducing mixed alcohols from syngas, wherein the catalyst containseither molybdenum or tungsten, in addition to either cobalt or nickel,both components being in sulfided form. Stevens and Conway emphasizethat it is not necessary for their invention that any particularstoichiometric metal sulfide be present. Sulfided cobalt is oftenassigned to CoS in the literature. Further, Stevens and Conway statethat no advantage is realized by the presence of sulfur in the feed.

U.S. Pat. No. 4,675,344 (Conway et al.) describes a method forcontrolling the ratio of methanol to higher alcohols by adjusting theconcentration of a sulfur-releasing compound in the feed to a reactorcontaining alkali-promoted MoS₂ catalysts. Conway teaches that suchcatalysts should exclude Group VIII elements, such as cobalt, to realizethe selectivity benefit of sulfur addition.

Murchison et al. discuss the use of cobalt-molybdenum sulfides formixed-alcohol synthesis in volumes 2 (pages 626-633) and 5 (pages256-259) of the Proceedings of the 9th International Congress onCatalysis (1988). Murchison stated that cobalt (or nickel) molybdenumsulfide materials could be operated without added H₂S. On page 257,Murchison stated that “[t]he effect of H₂S in increasing the chainlength of the alcohols is very specific for the alkalinized molysulfide, both supported and unsupported. The addition of cobalt to thecatalyst results in higher molecular weight alcohols without H₂Saddition and makes the catalyst selectivity substantially independent ofthe H₂S of the feed . . . .” During the discussion at the 9thInternational Congress on Catalysis, as recorded at page 258, aquestioner commented that “Santiestaban et al. indicate carbides are notformed” and poses a question, in response to which Murchison stated“[t]here is certainly no problem in long term stability without H₂S ifone is not concerned with maximizing C₂₊ alcohols. The XRD and XPS workwe have done has not shown any carbide formation for the sulfidedcatalysts.” Murchison teaches that Co/Mo sulfides will be stable foralcohol synthesis in the absence of H₂S and that carbides do not form asthe catalyst acquires operating time on stream.

The existing art provides little, if any, information concerningchemical or physical characteristics that tend to correlate with theperformance of cobalt-molybdenum-sulfide alcohol-synthesis catalysts,including Co—Mo—S, and similar catalyst systems comprising Ni and/or W.Particularly absent is information relating to preferred amounts ofsulfur, on a stoichiometric basis, relative to other major componentspresent.

Furthermore, the existing art does not provide guidance with respect tomaintain catalytic stability (in sulfided systems) for long periods oftime. Yet, catalyst lifetime and stability (i.e., the maintenance ofactivity and selectivity) are critical from a commercial point of view,for economic reasons.

In light of these shortcomings in the art, what are needed are methodsof making preferred sulfided catalyst compositions, methods of usingthese catalyst compositions, and methods of maintaining sufficientactivity and sulfide content to convert syngas into alcohols, such asethanol.

SUMMARY OF THE INVENTION

In some variations, this invention provides methods of producing atleast one C₁-C₄ alcohol from syngas, the method comprising:

(a) providing a reactor including a catalyst composition comprisingcobalt, molybdenum, and sulfur, wherein at least some of the cobalt andsome of the sulfur are present as a cobalt-sulfur association having amolar ratio of sulfur to cobalt (S:Co), calculated by assuming allmolybdenum is present as MoS₂;

(b) flowing syngas into the reactor at conditions effective to produceat least one C₁-C₄ alcohol; and

(c) injecting additional sulfur, or a compound containing sulfur, intothe reactor in an amount that is sufficient to maintain at least some ofthe cobalt in a sulfided state, and is further sufficient to maintainthe molybdenum in a completely sulfided state.

The additional sulfur injected can be contained in one or more compoundsselected from the group consisting of elemental sulfur, hydrogensulfide, dimethyl sulfide, diethyl sulfide, dimethyl disulfide, anyisomers of dibutyl polysulfide (such as ditertbutyl polysulfide), anyisomers of dioctyl polysulfide, diphenyl polysulfide, dicyclohexylpolysulfide, methylthiol, ethylthiol, cysteine, cystine, methionine,potassium disulfide, cesium disulfide, and sodium disulfide.

In some variations, this invention provides a method for maintainingcatalyst stability while producing at least one C₁-C₄ alcohol fromsyngas, the method comprising:

(a) providing a reactor including a catalyst composition comprisingcobalt, molybdenum, and sulfur;

(b) flowing syngas into the reactor at conditions effective to produceat least one C₁-C₄ alcohol; and

(c) injecting additional sulfur, or a compound containing sulfur, intothe reactor, in an amount that is sufficient to inhibit the formation ofcobalt carbides or molybdenum carbides under the conditions effective toproduce at least one C₁-C₄ alcohol.

In preferred embodiments, step (c) inhibits the formation of cobaltcarbides, such as crystalline Co₂C. In preferred embodiments, step (c)inhibits the formation of molybdenum carbides. In some embodiments, step(c) prevents any formation of cobalt carbides or molybdenum carbides.The additional sulfur provided in step (c) can maintain at least some ofthe cobalt in a sulfided state. Also, the additional sulfur canmaintains the molybdenum in a sulfided state.

In some embodiments, the method includes maintaining, for at least 1000hours, preferably at least 5000 hours, and more preferably at least10,000 hours on-stream, one or more parameters selected from the groupconsisting of CO conversion, ethanol selectivity, total alcoholselectivity, total alcohol productivity, and methane selectivity.

Certain embodiments include an additional step of recovering sulfurdownstream of the reactor and recycling at least a portion of the sulfurinto the reactor.

Other variations of the present invention provide a method ofaccelerated aging of a sulfided catalyst for the conversion of syngas toalcohols, the method comprising:

(a) providing a test reactor including a test catalyst containingsulfur;

(b) flowing syngas into the test reactor at conditions effective toproduce an alcohol; and

(c) injecting a suitable aging accelerant into the test reactor, whereinthe aging accelerant is capable of causing sulfur loss from the testcatalyst at a rate that is faster than the rate in the absence of theaging accelerant.

The aging accelerant can be methanol, or any other suitable chemicalthat causes sulfur loss. Methanol is preferred, in some embodiments. Themethanol can be injected in step (c) at about the equilibrium amount inaccordance with the methanol/syngas reaction equilibrium under theconditions in step (b).

The accelerated-aging method can be conducted for a test time selectedfrom about 1-200 hours, such as about 10-100 hours. The accelerationfactor should be greater than unity and can be, in various embodiments,at least 5, 10, 20, or more.

The accelerated-aging method preferably includes measuring at least oneparameter of interest at a plurality of times during operation of thetest reactor, to generate a test response. The parameter of interest canbe selected from the group consisting of CO conversion, ethanolselectivity, total alcohol selectivity, total alcohol productivity,methane selectivity, and sulfur concentration exiting the test reactor.Other parameters can be used, as well.

In some embodiments, the test response includes at least one correlationselected from the group consisting of decreasing CO conversion,decreasing ethanol selectivity, decreasing total alcohol selectivity,decreasing total alcohol productivity, increasing methane selectivity,and increasing sulfur concentration exiting the test reactor. Someembodiments further include characterizing the test catalyst bypredicting the lifetime or stability of a commercial catalyst withsubstantially the same composition as the test catalyst.

Some variations provide a method of characterizing a plurality ofsulfided catalysts, wherein each catalyst composition is a distinctcatalyst that is independently subjected to the following steps:

(a) providing a test reactor suitable for evaluating each of thesulfided catalysts;

(b) for each of the sulfided catalysts, flowing syngas into the testreactor at conditions effective to produce an alcohol; and

(c) for each of the sulfided catalysts, injecting a suitable agingaccelerant into the test reactor, wherein the aging accelerant iscapable of causing sulfur loss from each of the sulfided catalysts at arate that is faster than the rate in the absence of the agingaccelerant.

Some variations provide a method of characterizing performance of asulfided catalyst for the conversion of syngas to alcohols under aplurality of process conditions, the method comprising:

(a) providing a test reactor suitable for evaluating the sulfidedcatalyst;

(b) for each of the plurality of process conditions, flowing syngas intothe test reactor at conditions effective to produce an alcohol; and

(c) for each of the plurality of process conditions, injecting asuitable aging accelerant into the test reactor, wherein the agingaccelerant is capable of causing sulfur loss from each of the sulfidedcatalysts at a rate that is faster than the rate in the absence of theaging accelerant.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a graph depicting the effect of catalyst type and reactortemperature on experimental total-liquids yield.

FIG. 2 is a graph depicting the effect of catalyst type and reactortemperature on experimental ethanol yield.

FIG. 3 is a chart showing S:Co molar ratios associated with certainpreferred catalyst compositions.

FIG. 4 is a chart showing S:Co molar ratios associated with certainpreferred catalyst compositions.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

This description will enable one skilled in the art to make and use theinvention, and it describes several embodiments, adaptations,variations, alternatives, and uses of the invention, including what ispresently believed to be the best mode of carrying out the invention. Asused in this specification and the appended claims, the singular forms“a,” “an,” and “the” include plural referents unless the context clearlyindicates otherwise. Unless defined otherwise, all technical andscientific terms used herein have the same meaning as is commonlyunderstood by one of ordinary skill in the art to which this inventionbelongs.

Unless otherwise indicated, all numbers expressing reaction conditions,stoichiometries, concentrations of components, and so forth used in thespecification and claims are to be understood as being modified in allinstances by the term “about.” Accordingly, unless indicated to thecontrary, the numerical parameters set forth in the followingspecification and attached claims are approximations that may varydepending at least upon the specific analytical technique. Any numericalvalue inherently contains certain errors necessarily resulting from thestandard deviation found in its respective testing measurements.

The present invention will now be described by reference to thefollowing detailed description, which characterizes some preferredembodiments but is by no means limiting.

For present purposes, “catalyst composition” means a composition of acatalytic material that is not activated. An “activated catalystcomposition” is a composition of a catalytic material that is suitablyactivated (or regenerated). By “activated” it is meant that the catalystis exposed to conditions (such as, but not necessarily, reactorconditions) that render it more suitable for its intended purpose, whichin this case means the conversion of syngas to alcohols.

Base promoters can enhance the production of alcohols from syngas. By“base promoter” it is meant one or more metals that promote theproduction of alcohols. Base promoters may be present in free orcombined form. The base promoter can be present as a metal, oxide,carbonate, hydroxide, sulfide, as a salt, in a compound with anothercomponent, or some combination of the above.

It has been discovered that preferred variants of catalyst compositionsfor converting syngas to alcohols (e.g., C₁-C₄ alcohols) comprisecobalt-molybdenum-sulfide powders which have certain characteristicchemical signatures. These preferred catalyst compositions arerelatively rich in sulfur. Specifically, the amount of sulfur present inpreferred catalysts is higher than would be expected by a skilledartisan, based on typical oxidation numbers of cobalt and molybdenum insulfide compounds.

In some embodiments, the amount of sulfur present is in excess of thatexpected if cobalt occurs as CoS₂ and molybdenum occurs as MoS₂. In somepreferred embodiments, the amount of sulfur present is in excess of thatexpected if cobalt occurs as Co₃S₄ and molybdenum occurs as MoS₂, aswill be described in more detail below and in Examples 1 and 2.

Additionally, preferred compositions of cobalt-molybdenum-sulfidealcohol-synthesis catalysts are relatively unreactive toward gentleleaching into non-oxidizing aqueous mineral acids, such as hydrochloricacid. Furthermore, preferred variants of cobalt-molybdenum-sulfidecatalysts are slightly more reactive toward sulfur leaching intosolvents such as chloroform, as compared to less-preferred catalystcompositions.

As used herein, chloroform leaching of elemental sulfur refers to ananalytical extraction of the sulfur into substantially pure chloroform(CHCl₃), conducted at a temperature selected from about 20° C. to about55° C. or higher, and preferably at about 55° C. As is known, a varietyof solvents are capable of extracting elemental sulfur into solution. Itis preferable, but not critical, that chloroform is used. Other solventsthat can be effective include toluene, methylene chloride, xylenes,benzene, acetone, carbon tetrachloride, and carbon disulfide. Somecompositions of the present invention will be described in terms ofchloroform leaching, and it will be appreciated that similar results canbe obtained by leaching into other solvents effective for elementalsulfur.

As used herein, hydrochloric acid leaching of a metal refers to ananalytical extraction of the metal into a solution of 3N HCl, conductedat room temperature (such as about 25° C.) or at higher temperature(such as about 90° C.). Other acids can be effective. Generally, amoderately strong, non-oxidizing mineral acid is preferred. For example,dilute solutions of one or more acids selected from HBr, HI, HBF₄, orHPF₆ can be used. Preferably, acid concentrations for the leaching testsare low enough to avoid possible total digestion of the material. InHCl, which is preferred, an additional role of chloride is thought tostabilize oxospecies of molybdenum in the leachate with respect toreprecipitation. It is noted that a metal may be leached innon-elemental forms, such as aqueous cations or aqueous salts.

In some embodiments of Co—Mo—S catalyst compositions provided by thepresent invention, sulfur is present in a total (free or combined form)amount of at least 40 wt % of the catalyst composition. In somepreferred embodiments, total sulfur is between 42-44 wt % of thecomposition.

Preferred compositions do not contain very much elemental sulfur(typically regarded as S₈); i.e., they are not a mere physical mixtureof sulfur with the other elements present. A non-zero amount ofelemental sulfur can be present in preferred compositions. Namely,favored sulfided catalysts include elemental sulfur in an amount of atleast about 100 ppm, calculated on a total-catalyst weight basis. Theconcentration of elemental sulfur is preferably between about 150-5000ppm, more preferably between about 300-1000 ppm. Amounts higher than5000 ppm of elemental sulfur can be effective from a catalysisstandpoint, but there are practical concerns. For example, high levelsof elemental sulfur in the compositions can melt and/or sublime in thecatalyst bed, leading to operational problems. High levels of elementalsulfur could also lead to undesired formation of hydrogen sulfide orcarbonyl sulfide.

The amount of elemental sulfur present in preferred catalysts can alsobe related to convenient chloroform leaching tests as described above.In certain embodiments, at least about 0.02% (but preferably not morethan about 0.1%) of the total sulfur present is capable of leaching intochloroform. It is preferable that at least about 0.05% of the sulfur becapable of leaching into chloroform.

Preferred catalyst compositions for converting syngas into alcohols arehighly sulfided, with cobalt associated with sulfide. In someembodiments, dispersed and crystalline CoS₂ is present in thesecatalysts. It is known that high-valency transition metals can oxidizesulfur to disulfide (S₂ ²⁻) or even polysulfide species, with associatedreduction at the metal center. Polysulfides are anions with the generalformula S_(n) ²⁻ (n>2) and the general structure ⁻SS_(n-2)S⁻.

The molar ratio of sulfur to cobalt (“S:Co”), given an initialassignment of sulfur to molybdenum to yield MoS₂, is regarded as animportant parameter. As used herein, S:Co is calculated after assigningsome of the sulfur to molybdenum by assuming all molybdenum is presentin the catalyst composition as MoS₂. The S:Co molar ratio can optionallybe calculated after subtracting sulfur that is capable of leaching intochloroform (or a similarly effective solvent), which will tend toaccount for elemental sulfur. The S:Co molar ratio can also optionallybe calculated after subtracting sulfur that is capable of leaching into3 N HCl (or a similarly effective dilute acid), which will tend toaccount for sulfur in the form of sulfates, sulfites, persulfates,hyposulfites, and the like. In some embodiments, the S:Co molar ratiocan be calculated to account for all forms of sulfur that are soluble in(i.e., capable of leaching into) both chloroform and 3 N HCl. Preferredcompositions do not have excessive amounts of these forms of sulfur, sothe calculated S:Co molar ratios are typically not especially sensitiveto the exclusion of sulfur species that are soluble in chloroform and/or3 N HCl.

The S:Co molar ratio in the cobalt-sulfur association is at least about1.2. Preferably, the molar ratio S:Co is at least about 1.5, and morepreferably at least about 2.0. In some embodiments, S:Co is betweenabout 2.0 and about 4.0. For example, for illustration purposes only,various specific embodiments of the invention can employ S:Co ratios ofabout 1.2, 1.3, 1.35 (i.e., slightly higher than what would be expectedif cobalt were present as Co₃S₄), 1.4, 1.5, 1.75, 1.95, or 2.0. Variousother specific embodiments can use S:Co ratios of about 2.05, 2.1, 2.2,2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or 3.0. In other embodiments, S:Coratios can exceed 3.0, such as up to and including about 4.0 or higher.These higher S:Co ratios can occur, for instance, when polysulfideanions are associated with cobalt.

In some embodiments of Co—Mo—S catalyst compositions, cobalt is presentin an amount between about 3-21 wt %, preferably between about 10-16 wt%, and more preferably between about 13-15 wt % (wherein wt % is weightpercent based on the total catalyst composition). In some embodiments ofCo—Mo—S catalyst compositions, molybdenum is present in an amountbetween about 33-56 wt %, preferably between about 35-50 wt %, and morepreferably between about 40-45 wt %.

In preferred embodiments, the molar ratio of molybdenum to cobalt,Mo:Co, can generally be between about 1 and about 20, preferably betweenabout 1.5 and about 8, and more preferably about 2.

The mass fraction of total sulfur (i.e. sulfur in free or combined form)is preferably greater than 40 wt % for catalyst compositions when theMo:Co mole ratio is about 2. Alcohol-synthesis catalysts can, however,use Mo:Co mole ratios different from 2, as described above. As the Mo:Comole ratio varies, the desirable mass fraction of sulfur will alsopreferably vary. In preferred embodiments, the catalyst compositionincludes sufficient sulfur so that all Mo can occur as MoS₂, withadditional sulfur so as to maintain cobalt in a sulfided state.

It is preferable that the catalyst composition includes sulfur in anoxidation state that is relatively high, for the sulfur in associationwith cobalt. In some embodiments, the average oxidation number forsulfur in association with cobalt is greater than −2, preferably atleast about −1.5, and more preferably about −1. Average sulfur oxidationstates can be in the range of −2 to −1 or higher, according to thepresent invention, for the sulfur in association with cobalt.

In Co₃S₄, wherein S:Co=1.33, the oxidation number of cobalt is both +2and +3 (formally Co₃S₄ is [Co(II)][Co(III)]₂S₄). The average oxidationstate of sulfur in Co₃S₄ is −2. In CoS₂, wherein S:Co=2, the oxidationnumber of cobalt is +2 and the sulfur oxidation number is −1.Cobalt-sulfur associations having higher S:Co molar ratios are expectedto have higher (less negative) sulfur oxidation numbers. In light of thepreferred S:Co molar ratios as described above, preferred embodiments ofthe catalyst compositions of the invention will include at least aportion of sulfur in the −1 oxidation state.

The amount and nature of cobalt present in preferred catalysts can berelated to convenient hydrochloric acid leaching tests as describedabove. In some embodiments, less than about 8% of the total cobaltpresent is capable of leaching into a 3N HCl solution. It is preferablethat less than about 5%, 3%, 2%, 1%, or less (including substantiallynone) of the total cobalt is capable of leaching into 3N HCl.“Substantially none” means that no metal is measured by standarddetection techniques, but a small amount may in fact be present in the3N HCl leachate.

The amount and nature of molybdenum present in preferred catalysts canbe related as well to these convenient hydrochloric acid leaching tests.In some embodiments, less than about 1.0% of the total molybdenumpresent is capable of leaching into a 3N HCl solution. It is preferablethat less than about 0.5%, 0.3%, 0.2%, 0.1%, or less (includingsubstantially none) of the total molybdenum is capable of leaching into3N HCl.

Other aspects of the invention relate to preferred sulfidestoichiometries pertaining to nickel-molybdenum-sulfide,cobalt-tungsten-sulfide, and nickel-tungsten-sulfide catalystcompositions. When Ni is employed rather than Co, the amount of sulfurpresent will be in excess of that which would be expected if Mo occursas MoS₂ and Ni as NiS. When tungsten is used rather than molybdenum, theamount of sulfur present will be in excess of that which would occur ifcobalt were present as CoS, or nickel as NiS, and tungsten present asWS₂.

Some embodiments of the present invention provide a catalyst compositionfor catalyzing the conversion of syngas into alcohols, the compositioncomprising sulfur, a first element or plurality of elements E1 and asecond element or plurality of elements E2, wherein: E1 is cobalt and/ornickel; E2 is molybdenum and/or tungsten; at least some of E1 and someof the sulfur are present as an E1-sulfur association; and the molarratio of sulfur to E1 (S:E1) in the association is at least 1.2, themolar ratio S:E1 calculated after assigning some of the sulfur to E2 byassuming all E2 is present in the composition as E2S₂, and optionallyafter subtracting any sulfur that is soluble in chloroform and/or 3 NHCl. In certain embodiments, the molar ratio S:E1 is at least 1.5,preferably between about 2.0 and about 4.0, selected in a similar manneras described above for S:Co.

E1 can be present in an amount between about 2 wt % and about 25 wt %,and E2 can be present in an amount between about 25 wt % and about 95 wt% of the composition. In some embodiments, E1 is present in an amountbetween about 10-25 wt % of the composition, and E2 is present in anamount between about 25-60 wt %.

In some embodiments, total sulfur is present in a total amount of atleast 30 wt % of the composition. This total sulfur preferably includesat least 100 ppm elemental sulfur. In certain preferred embodiments, atleast 0.02% of the sulfur is capable of leaching into chloroform at 25°C. In preferred embodiments, less than about 5% of E1 and less thanabout 0.5% of E2 is capable of leaching into a 3N HCl solution at 25° C.

Generally, preferred Ni—Mo—S, Co—W—S, or Ni—W—S catalysts will besimilarly resistant toward leaching metals into gentle mineral acid, asare preferred Co—Mo—S catalysts. As will be appreciated by a skilledartisan, similar methods can be recited for catalysts containing complexmixtures, such as Co—Ni—Mo—W—S catalysts.

Aspects of the present invention also relate to methods of making thesecatalyst compositions. The catalytic species may be dispersed by methodsknown in the art. Examples include impregnation from solution followedby conversion to the sulfided species or intimate physical mixing. Oneor more of these methods may be used. It is preferred that at least twoof the catalytic components (i) Mo and/or W, (ii) Co and/or Ni, and(iii) S are intimately mixed. More preferably, all of these catalystcomponents are substantially intimately mixed.

In some embodiments, the catalyst composition further includes at leastone base promoter which can increase selectivities to alcohols fromsyngas. In some embodiments, at least one base promoter includes one ormore elements selected from the group consisting of potassium, rubidium,cesium, barium, strontium, scandium, yttrium, lanthanum, or cerium, infree or combined form.

The base promoter is preferably at least present at a level sufficientto render the catalyst more basic. The base promoter is generallypresent in an amount of at least about 0.01 wt %, with metal promoterscalculated as if a free element in the catalyst. Preferably, the basepromoter is present in an amount of at least 0.1 wt %, more preferablybetween about 1 wt % and 20 wt %.

The base promoter may be added as an ingredient to a catalytic componentor to a support, or may be part of one of the catalytic components or asan integral part of the support. The base promoter may be added to theactive catalytic element prior to, during, or after the formation of thesulfide. For example, physical mixing or solution impregnation may beemployed.

In certain embodiments of the present invention, ammoniumtetrathiomolybdate can by made by addition of ammonium sulfide solutionor hydrogen sulfide gas to a solution of a soluble molybdate, such as(for example) ammonium heptamolybdate. To this solution, cobalt acetatesolution may be added to provide a suspension wherein the Mo:Co ratio isabout 2. Without being limited by any particular theory, it is presentlybelieved that these embodiments take advantage of the insolubility ofthe [NH₄ ⁺]₂[Mo₂CoS₈ ²⁻] salt.

If Mo:Co mole ratios different from two are desired, some [NH₄⁺]₂[Mo₂CoS₈ ²⁻] salt still forms. When cobalt is in excess, it maycoprecipitate by assuring an excess of sulfide anion is present at thetime of cobalt precipitation, resulting in an intimately mixedprecipitate. This precipitate comprises an amorphous cobalt sulfide and[NH₄ ⁺]₂[Mo₂CoS₈ ²⁻] salt. If Mo is desired to be present in excess ofMo:Co=2:1, its precipitation may be favored by controlling thetemperature of coprecipitation at a temperature lower than about 50° C.Solubility of ammonium tetrathiomolybdate is rather strongly temperaturedependent, decreasing at lower temperatures. Nickel and tungsten reactwith very similar trends.

To the [NH₄ ⁺]₂[Mo₂CoS₈ ²] precipitate, an aqueous solution of, forexample, an acetate salt of a lanthanide-series metal or of barium orstrontium may be added by incipient-wetness impregnation. Thecomposition is then calcined under inert conditions, in certainembodiments. “Inert conditions” with respect to calcining means that (i)the atmosphere at the inlet to the calciner (or other apparatuseffective for calcining Co—Mo—S materials) is substantially free of O₂and H₂O, and further that (ii) separation of H₂O and volatile components(such as NH₃, S₈, and the like) from the solid catalyst phase isefficient. N₂ and Ar, if suitably free of contaminating water andoxygen, represent suitable carrier gases for the calcinations.

Alternately, the ammonium cobalt thiomolybdate may be calcined underinert conditions prior to addition of the base promoter. In this case,it is typically convenient to grind, under a substantially inertatmosphere, a salt (e.g., an acetate or carbonate salt) of a basepromoter such as potassium or cesium.

The catalyst can take the form of a powder, pellets, granules, beads,extrudates, and so on. When a catalyst support is optionally employed,the support may assume any physical form such as pellets, spheres,monolithic channels, etc. The supports may be coprecipitated with activemetal species; or the support may be treated with the catalytic metalspecies and then used as is or formed into the aforementioned shapes; orthe support may be formed into the aforementioned shapes and thentreated with the catalytic species.

In embodiments of the invention that employ a catalyst support, thesupport is preferably (but not necessarily) a carbon-rich material withlarge mesopore volume, and further is preferably highlyattrition-resistant. One carbon support that can be utilized is“Sibunit” activated carbon (Boreskov Inst. of Catalysis, Novosibirsk,Russia) which has high surface area as well as chemical inertness bothin acidic and basic media (Simakova et al., Proceedings of SPIE—Volume5924, 592413, 2005). An example of Sibunit carbon as a catalyst supportcan be found in U.S. Pat. No. 6,617,464 (Manzer).

The present invention also relates to use of catalyst compositions. Insome embodiments of the invention, a reactor is loaded with a catalystcomprising a composition as described herein. A process streamcomprising syngas is fed into the reactor at conditions effective forproducing alcohols from the syngas.

In some embodiments, conditions effective for producing alcohols fromsyngas include a feed hydrogen/carbon monoxide molar ratio (H₂/CO) fromabout 0.2-4.0, preferably about 0.5-2.0, and more preferably about0.5-1.5. These ratios are indicative of certain embodiments and are notlimiting. It is possible to operate at feed H₂/CO ratios less than 0.2as well as greater than 4, including 5, 10, or even higher. It iswell-known that high H₂/CO ratios can be obtained with extensive steamreforming and/or water-gas shift in operations prior to thesyngas-to-alcohol reactor.

In embodiments wherein H₂/CO ratios close to 1:1 are desired for alcoholsynthesis, partial oxidation of the carbonaceous feedstock can beutilized. In the absence of other reactions, partial oxidation tends toproduce H₂/CO ratios close to unity, depending on the stoichiometry ofthe feedstock.

When, as in certain embodiments, relatively low H₂/CO ratios aredesired, the reverse water-gas shift reaction (H₂+CO₂→H₂O+CO) canpotentially be utilized to consume hydrogen and thus lower H₂/CO. Insome embodiments, CO₂ produced during alcohol synthesis or elsewhere,can be recycled to the reformer to decrease the H₂/CO ratio entering thealcohol-synthesis reactor. Other chemistry and separation approaches canbe taken to adjust the H₂/CO ratios prior to converting syngas toalcohols, as will be appreciated. For example, certain commercialmembrane systems are known to be capable of selectively separating H₂from syngas, thereby lowering the H₂/CO ratio.

In some embodiments, conditions effective for producing alcohols fromsyngas include reactor temperatures from about 200-400° C., preferablyabout 250-350° C.; and reactor pressures from about 20-500 atm,preferably about 50-200 atm or higher. Generally, productivity increaseswith increasing reactor pressure. Temperatures and pressures outside ofthese ranges can be employed.

In some embodiments, conditions effective for producing alcohols fromsyngas include average reactor residence times from about 0.1-10seconds, preferably about 0.5-2 seconds. “Average reactor residencetime” is the mean of the residence-time distribution of the reactorcontents under actual operating conditions. Catalyst space times orcatalyst contact times can also be calculated by a skilled artisan andthese times will typically also be in the range of 0.1-10 seconds,although it will be appreciated that it is certainly possible to operateat shorter or longer times.

In general, the specific selection of catalyst configuration (geometry),H₂/CO ratio, temperature, pressure, residence time (or feed rate), andother reactor-engineering parameters will be selected to provide aneconomical process. These parameters are not regarded as critical to thepresent invention. It is within the ordinary skill in the art toexperiment with different reactor conditions to optimize selectivity toa particular product or some other parameter.

Product selectivities can be calculated on a carbon-atom basis.“Carbon-atom selectivity” means the ratio of the moles of a specificproduct to the total moles of all products, scaled by the number ofcarbon atoms in the species. This definition accounts for themole-number change due to reaction. The selectivity S_(j) to generalproduct species C_(xj)H_(yj)O_(zj) is

$S_{j} = \frac{x_{j}F_{j}}{\sum\limits_{i}{x_{i}F_{i}}}$wherein F_(j) is the molar flow rate of species j which contains x_(j)carbon atoms. The summation is over all carbon-containing species(C_(xi)H_(yi)O_(zi)) produced in the reaction.

In some embodiments, wherein all products are identified and measured,the individual product selectivities sum to unity (plus or minusanalytical error). In other embodiments, wherein one or more productsare not identified in the exit stream, the selectivities can becalculated based on what products are in fact identified, or insteadbased on the conversion of reactants. In the latter case, theselectivities may not sum to unity if there is some mass imbalance.Nevertheless, this method can be preferable as it tends to determinemore accurate selectivities to identified products when it is suspectedthat at least one reaction product is not measured.

“CO₂-free carbon-atom selectivity” or “CO₂-free selectivity” mean thepercent of carbon in a specific product with respect to the total carbonconverted from carbon monoxide to some product other than carbondioxide. It is the same equation above for S_(j), except that i≠CO₂ andj≠CO₂.

In various embodiments of the present invention, the product stream fromthe reactor may be characterized by CO₂-free selectivities of about10-40% to methanol and about 20-60% or higher to ethanol. In somepreferred embodiments, the ethanol CO₂-free selectivity is higher,preferably substantially higher, than the methanol CO₂-free selectivity,such as a CO₂-free selectivity ratio of ethanol/methanol in the productof about 1.0, 1.5, 2.0, 2.5, 3.0, or higher. The product stream can alsocontain more methanol than ethanol, on either a mole basis or acarbon-atom basis, in certain embodiments. The CO₂-free selectivityratio of ethanol to all other alcohols is preferably at least 1, morepreferably at least 2.

The product stream from the reactor may include up to about 25% CO₂-freeselectivity to C₃₊ alcohols, and up to about 10% to other non-alcoholoxygenates such as aldehydes, esters, carboxylic acids, and ketones.These other oxygenates can include, for example, acetone, 2-butanone,methyl acetate, ethyl acetate, methyl formate, ethyl formate, aceticacid, propanoic acid, and butyric acid.

Another aspect of the invention relates to methods for activating, orotherwise generating, preferred activated catalyst compositions. In someembodiments, an activated catalyst composition is prepared by firstproviding a starting catalyst composition comprising cobalt, molybdenum,and sulfur, wherein at least some of the cobalt and some of the sulfurare present as a cobalt-sulfur association, and wherein the molar ratioof sulfur to cobalt (S:Co) in the association is at least 1.2, the molarratio S:Co calculated by assuming all molybdenum is present in thecatalyst composition as MoS₂. This starting catalyst composition is thensubjected to a stream of syngas under suitable activation conditions,preferably in situ within the reactor, such that the S:Co molar ratio(calculated in the same way as for the starting catalyst composition)decreases to a ratio that is at least somewhat lower than the S:Co molarratio in the starting catalyst composition. In various embodiments, theS:Co molar ratio decreases to about 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.9,0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, or even less, provided at leastsome of the cobalt remains in a sulfided state.

In certain embodiments of this aspect relating to catalyst activation,with reference to the above-described hydrochloric acid leaching tests,a first amount of total cobalt contained in the starting catalystcomposition is capable of leaching into a 3N HCl solution, and a secondamount of total cobalt contained in the activated catalyst compositionis capable of leaching into a 3N HCl solution. Preferably, the secondamount of cobalt is greater than the first amount of cobalt that canleach. For example, when less than about 5% of the total cobalt presentin the starting catalyst composition can leach into a 3N HCl solution,more than about 5% of the total cobalt present in the activated catalystcomposition can leach into a 3N HCl solution. When less than about 1% ofthe total cobalt in the non-activated catalyst composition can leachinto a 3N HCl solution, more than about 1% of the total cobalt in theactivated catalyst composition can leach into such a solution.

During activation, the catalyst can become more reduced, with evolutionof various light sulfur compounds such as H₂S, CH₃SH, CH₃SCH₃, CH₃CH₂SH,and the like. In some variations, it can be beneficial (but is by nomeans necessary) to add sulfide back to the activated or operatingcatalyst composition to compensate for the sulfur that evolves duringactivation or operation. Yet another aspect of the present inventionprovides methods to maintain certain sulfide levels in the activatedcatalyst compositions. In these methods, sulfur or a compound containingsulfur can be injected into the reactor, in an amount that is sufficientto maintain both the cobalt and the molybdenum in sulfided states.

In some embodiments of this aspect, additional sulfur is injected so asto control the molar ratio S:Co to between about 1.2 to about 2 orhigher, up to about 4. Catalyst samples can be analyzed to measure S:Coand, if needed, additional sulfur can be introduced. Alternately,experiments can be separately conducted to establish that additionalsulfur is necessary at certain times, or as a continuous injection inprescribed amounts, or some other program, in order to control(maintain) the S:Co ratio. S:Co is “measured and controlled” within themeaning herein whether the measurements are made prior to, or during,reactor operation.

In some embodiments, additional sulfur can be introduced by injecting,in dissolved form or another effective form, one or more compoundsselected from elemental sulfur, hydrogen sulfide, dimethyl sulfide,diethyl sulfide, dimethyl disulfide, any isomers of dibutyl polysulfide(such as ditertbutyl polysulfide), any isomers of dioctyl polysulfide,diphenyl polysulfide, dicyclohexyl polysulfide, methylthiol, ethylthiol,cysteine, cystine, methionine, potassium disulfide, cesium disulfide,and/or sodium disulfide. Various isomers of these compounds may be used.For example, cysteine may be present as L-cysteine, D-cysteine, orD,L-cysteine mixtures. This list of potential sulfur-containingcompounds is merely exemplary and by no means limits the scope of theinvention.

For the purpose of adding to the reactor, one or more of thesesulfur-containing compounds can be dissolved in, for example, toluene orother organic solvents. For the disulfides of potassium, sodium, orcesium, effective solvents may be selected from alcohols, short-chainpolyethylene glycols, acetonitrile, DMF, DMSO, or THF, for example.

Here, “injecting” sulfur can mean feeding sulfur into the reactor at theentrance, or introducing sulfur into the catalyst bed in any other way.Injecting includes introduction of sulfur as part of a syngas feedstream that comprises sulfur. Injecting can also include shutting downthe normal operation of the reactor (syngas to alcohols) and thenflowing a sulfur-containing compound through the catalyst bed in somefashion, to cause a change in the S:Co ratio.

Some variations of the present invention are premised on the discoverythat extended operation of an alkali-promoted Co/Mo/S catalyst, in theabsence of co-fed hydrogen sulfide, leads to substantial loss of sulfurfrom the catalyst. Furthermore, it has been realized that extendedcatalyst operation results in a substantial fraction of Co and Mooccurring as non-crystalline carbides, according to elemental analysis.For example, after 1000 hours or more on stream, the formation ofcrystalline Co₂C is readily observed by XRD.

Carbide formation in Co/Mo/S catalysts, whether the metal carbide iscrystalline or non-crystalline, is not favorable and should be avoidedwhen alcohols are desired products. Cobalt carbide and/or molybdenumcarbide tend to reduce CO conversion, reduce ethanol selectivity, reducetotal alcohol selectivity, and increase methane selectivity, at the sameprocess conditions suitable for ethanol synthesis from syngas whencarbides are not present.

In order to operate a stable alcohol-synthesis process for acommercially reasonable amount of time, such as in excess of 1000 hours,the presence of a sulfiding agent in the feed, or in another stream intothe reactor, is very beneficial. A sulfiding agent is desired to operatefor an extended period of time without formation of less active and lessselective transition-metal carbides. Also, a sulfiding agent isbeneficial to operate for an extended period of time withoutdeterioration of ethanol selectivity or formation rates (ethanolproductivity).

In some embodiments, alkali-promoted Co/Mo/S catalysts require ongoingsulfur feeding and optionally sulfur recycle. For example, H₂S oranother suitable sulfur-releasing compound could be introduced withsyngas fed to the reactor. Dimethyl disulfide (DMDS) is preferred, insome embodiments. It is expected that DMDS will convert, in the presenceof H₂, to H₂S and CH₄ over alkali-promoted Co/Mo/S catalysts. The H₂Sgenerated in-situ can help maintain sulfide levels in the catalysts.

In some embodiments, sulfur compounds result in the product, and aportion or all of these sulfur compounds can be recycled to an upstreampart of the process, such as into the alcohol-synthesis reactor. Thismode of operation can reduce costs associated with fresh sulfidingagents as well as minimize sulfur disposal costs.

Some carbonaceous feedstocks that can produce syngas (for use in thepresent invention) also contain sulfur. In some embodiments, sulfurcompounds can be recovered from the selected feedstock upstream of thealcohol-synthesis reactor, and these sulfur compounds can be used assulfiding agents. For example, sulfur compounds could be generatedduring devolatilization, extracted during syngas clean-up orconditioning, and so on.

Catalyst lifetime is an economically significant parameter. While thereare various reasons why a sulfided catalyst “ages” and loses stability,it will be recognized by a skilled artisan that sulfur loss is acritical component in catalyst lifetime. But it is not practical to testevery potential catalyst in long-term reactor operation. It thereforewould be desirable to establish a technique wherein catalyst aging canbe accelerated in a meaningful way. Certain variations of the presentinvention provide methods of “accelerated aging,” that is,characterizing or predicting catalyst stability over extended periods ofoperation—without actually operating reactors for extended periods.

In some embodiments, co-feeding syngas with methanol accelerates therate of sulfur loss. Sulfur loss can lead to carbide formation asdescribed herein, but these variations should not be limited by anyparticular theory or hypothesis, or by any specific fate ofinsufficiently sulfided metals.

Process conditions for accelerated aging can vary widely. The inventionis not limited to particular conditions but rather is intended topredict stability across ranges of conditions. Exemplary conditions foraccelerated aging of a Co/Mo/S/K catalyst are as follows: H₂/CO=2, 325°C., GHSV of 8500/hr, 1500 psig, recycle ratio=4, and a methanolinjection rate of about 25 mol/kg-cat/hr. The methanol injection ratecan vary from, for example, about 1-100 mol/kg-cat/hr, such as about10-50 mol/kg-cat/hr, in some embodiments. In certain embodiments, theamount of methanol injected is about the equilibrium amount (accordingto the methanol/syngas reaction equilibrium) at or near the entrance tothe catalytic reactor.

The amount of time necessary to establish a prediction of long-termstability can vary, depending on conditions employed and the nature ofthe catalyst being tested. The amount of time can also be a function ofthe desired degree of accuracy (e.g., rough screening versus detailedpredictions for scale-up). In some embodiments, the test time can beselected from about 1 hour to about 200 hours, e.g. about 10-100 hours.It can be preferable to test at constant conditions for at least about50 hours to detect aging. The minimum testing time should be that periodof time capable of detecting a statistically significant loss incatalyst activity.

An important outcome of accelerated-aging tests is the “accelerationfactor,” which means the enhancement in aging rate realized duringaccelerated aging by the methods described herein, compared to the agingrate that would result from actual extended operation. The accelerationfactor is calculated as the rate of sulfur loss from a test catalyst inthe presence of an aging accelerant divided by the rate of sulfur lossin the absence of the aging accelerant. This factor should at least beunity to realize a benefit. In various embodiments, the accelerationfactor can be at least about 2, 3, 4, 5, 8, 10, 15, 20, 25, 50, 75, 100or more.

An accelerated-aging test need not actually run for a length of timegiven by the predicted catalyst lifetime divided by the accelerationfactor. The testing time can actually be shorter. To illustrate, a testconducted for 50 hours with an acceleration factor of 20 would becapable of explicitly characterizing catalyst performance up until 1000hours under real conditions. Provided there is some detectable loss instability over this period of time, and a satisfactory correlation canbe established, performance can be predicted for periods well in excessof 1000 hours—such as 2,000, 5,000, 10,000 hours or more.

Many types of predictions can be used. For example, a threshold ethanolselectivity could be chosen, wherein the predicted catalyst lifetime isthe period of time up until the ethanol selectivity falls below thethreshold. It is noted that exact correlations are not necessary,provided there are trends during accelerated aging that can be utilizedto predict ultimate catalyst performance.

Methanol injection is useful as an aging accelerant in Co/Mo/S catalystsystems, but methanol is by no means the only species that can beemployed for this purpose. Any hydrocarbon, oxygenate, organic acid, orother functional group that is capable of removing sulfur from sulfidedmetals can be employed. It will be recognized that different agingaccelerants will have different efficiencies of sulfur removal and maycause other surface reactions that could serve to otherwise alter thecatalyst stability. A person of ordinary skill in the art can select anaging accelerant and conduct initial experiments to establish relevantcorrelations, such as is demonstrated in Example 7.

Accelerating aging can be beneficial to characterize multiple catalystcompositions in an effort to screen for commercially desirablematerials. Accelerating aging can also be beneficial to examinedifferent process conditions, to understand the impact on catalyst agingand lifetime. Finally, accelerating aging can be useful to prescribe aquantity of sulfur to be injected to maintain stability.

In some commercial embodiments, the levels of sulfur may need to varyover time. Accelerated again could allow one to establish a dynamicprofile of sulfur addition over the lifetime of a catalyst. Toillustrate, sulfur levels in the feed to a catalyst undergoingaccelerated aging could be adjusted systematically until catalyststability changes, thereby indicating an amount of sulfur compounds toemploy at various times.

EXAMPLES Example 1 Performance of Compositions RF-1 and RF-2

Two catalyst compositions are produced and given the designations RF-1and RF-2. Both compositions generally comprise Co—Mo—S and are producedin a similar manner, according to the description herein above, but theultimate compositions that are obtained are different. The synthesis ofRF-2 employs conditions that tend to exclude the atmosphere to a greaterextent than the conditions for synthesis of RF-1.

In separate experiments, RF-1 and RF-2 catalysts are loaded into areactor and tested for their capability to convert syngas into liquidproducts including ethanol. In these experiments, the primary variablesare catalyst type (RF-1 or RF-2) and reactor temperature (310° C., 325°C., or 345° C.). A full-factorial experimental design is carried out,with 2×3=6 experiments. These experiments are each controlled to 30% COconversion by adjusting space velocities.

FIG. 1 shows the impact of catalyst and temperature on total liquidyield. FIG. 2 depicts the ethanol yield versus temperature, calculatedas grams of liquid product per gram of catalyst per hour, for the twodifferent catalysts RF-1 and RF-2. Also analyzed (not shown) are otheralcohols including methanol, propanol, and butanol; water; and organicacids. From FIG. 2, it is experimentally observed that RF-2 is thesuperior catalyst of the two at any of the temperatures tested.

Example 2 Characterization of Compositions RF-1 and RF-2

The two catalyst compositions tested in actual reactors in Example 1,referred to as RF-1 and RF-2, are characterized in this example. Theanalysis for both compositions includes LECO S analysis, to determinetotal sulfur content; leaching the materials with chloroform, to assessthe amount of elemental sulfur present; and leaching with 3N HCl, toassess the amount of hydrophilic, soluble sulfur, cobalt, andmolybdenum. Three separate samples for each composition RF-1 and RF-2are analyzed.

The mass fractions of total cobalt and total molybdenum are essentiallythe same for both RF-1 and RF-2, while the mass fractions of totalsulfur are different (see tables below). The wt % numbers indicate themean±standard deviation of the measurements. At test value greater than0.05 implies that there is no statistical basis to assert thatdifferences exist, for that particular parameter, between RF-1 and RF-2.

Total Co (wt %) Total Mo (wt %) RF-1 14.43 ± 0.84 44.8 ± 2.2 RF-2 13.67± 0.48 42.0 ± 2.4 t test 0.09 0.07

Total S (wt %) RF-1 38.70 ± 0.80 RF-2 42.71 ± 0.44 t test 6.1 × 10⁻⁶

The amount of elemental sulfur (chloroform-leachable sulfur) is higherin RF-2 than in RF-1, as shown below. RF-2 is slightly more reactivetoward leaching of elemental sulfur than RF-1. This result is consistentwith a more highly sulfided, less hydrophilic or oxophilic material forcatalyst composition RF-2.

Elemental Sulfur (wt %) RF-1 0.0088 ± 0.0031 RF-2 0.0382 ± 0.0045 t test4.3 × 10⁻⁷

More cobalt and molybdenum from RF-1 leach into 3N HCl solution thanfrom RF-2. The amounts of sulfur that leach into 3N HCl are comparablefor the two materials.

Leachable Material into 3 Normal HCl Aqueous Solutions

wt % Leachable S wt % Leachable Co wt % Leachable Mo RF-1 0.365 ± 0.0741.49 ± 0.18  1.08 ± 0.17 RF-2 0.432 ± 0.023 0.402 ± 0.042 0.125 ± 0.15 ttest 0.08 1.1 × 10⁻⁵ 3.2 × 10⁻⁵

RF-2 is relatively non-reactive toward metal leaching by 3N HCl. Giventhe assumption that Mo is present as MoS₂, as described above, a molarS:Co ratio can be calculated and the degree of sulfidation can beassessed.

S:Co Mole Ratio RF-1 1.13 ± 0.27 RF-2 1.97 ± 0.25 t test 2.3 × 10⁻⁴

Given the results of Example 1 (e.g., FIG. 2) in conjunction with thecharacterizations in Example 2, preferential aspects of compositions forhigher-alcohol synthesis catalysts are revealed.

Example 3 Experimental Co:S Molar Ratios for Certain Preferred CatalystCompositions of the Invention

In this example, 18 distinct Co—Mo—S catalysts are synthesized in amanner experimentally similar to the procedure to synthesize RF-2 inExample 1. Due to imperfect process control, some variations incomposition arise. A representative reactor experiment at 325° C. and30% CO conversion (for reasons explained in Example 1) gives a liquidyield of about 0.21 g/g/hr and an ethanol yield of about 0.1 g ethanolper g catalyst per hour. With reference to the performance of RF-1 andRF-2, as shown in FIGS. 1 and 2, the performance of this single catalystwas measurably better than RF-1.

All 18 lots of catalyst in this example are analyzed by the sametechniques as described in Example 2. It is of interest to consider theS:Co molar ratio, given an initial assignment of sulfur to molybdenum toyield MoS₂.

FIG. 3 depicts the S:Co molar ratios across the 18 lots of catalystssynthesized in this example, wherein S:Co is calculated aftersubtracting elemental sulfur as determined by leaching into chloroformat room temperature. This ratio varies between about 2.2 and about 2.7,with an average of about 2.4.

FIG. 4 shows the S:Co molar ratios across the 18 lots of catalysts,wherein S:Co here subtracts the sulfur species (presumably primarilysulfate) soluble in 3 N HCl, as well as the sulfur that is soluble inchloroform. This ratio varies between about 2.2 and about 2.9, with anaverage of about 2.5. The lowest S:Co ratio observed here, 2.2, exceedswhat would be expected if the sulfided components are present only asMoS₂ and CoS₂. Furthermore, the sulfur-to-cobalt ratio is significantlyhigher than what would be expected if cobalt is present as CoS and/orCo₃S₄.

Example 4 Evolution of Co:S Molar Ratios During Alcohol Synthesis

In this example, a Co—Mo—S powder with Mo:Co=2 (mole basis) and S:Co=2.1(assuming Mo is present as MoS₂) is provided. This powder is compoundedwith K₂CO₃ such that Co:K=1 (mole basis), mixed with a binder, andformed into catalyst pellets. These pellets are loaded into reactors andoperated under alcohol-synthesis conditions for varying periods of timeas follows: sample A at 90 hours; sample B at 200 hours; and sample C at500 hours. The pellets are then discharged under inert conditions andsubjected to chemical analysis. Note that the three different samplesherein are run in different reactors.

Catalyst sample A has a S:Co ratio of about 1.4 (assuming that Mo occursas MoS₂), and 40-46% of the cobalt leaches into 3N HCl solution. SampleB has a S:Co ratio of about 0.5, and 50% of the cobalt leaches into 3NHCl solution. Sample C has a S:Co ratio of about 0.9, and 39-42% of thecobalt is extracted into 3N HCl.

It is therefore observed that a substantial fraction (about 40-50%) ofcobalt is extracted into 3HCl and the S:Co ratio varies from about 0.45to 1.4 even though, initially, S:Co was about 2.1 and only a smallportion (in the range of 0.5-7%) of cobalt leaches from the initialcatalyst. By contrast, 10% of the Co in RF-1 catalyst (Example 1)extracts into 3N HCl and the S:Co ratio in RF-1 catalyst is about 1.1. Alarge fraction (35-55%) of Co in catalytically used RF-2 catalyst isextractable into 3N HCl, while only 10% of Co in RF-1 is extractableinto 3N HCl.

Example 5 Bulk Chemical Properties of Co/Mo/S Catalysts After 3800 Hoursof Operation

Chemical analysis of alkali-promoted Co/Mo/S catalysts recovered from apilot reactor after about 3800 hr operation reveals substantial changesfrom fresh catalysts. Sulfur content is quite low. Compared withcatalysts aged between 50-500 hr, cobalt is less leachable. Carbonlevels are high. C:H ratios increase as one moves downbed. Cobaltcarbides may occur throughout the bed while molybdenum carbides mayoccur in the middle and bottom of the bed.

Seven samples of catalyst pellets (two top-bed, two mid-bed, threebottom-bed) are analyzed for total C, H, Co, Mo, S, and K. In addition,3N HCl leachable Co, Mo, and S are determined. As expected, Mo:Co isabout 2 and does not vary across the bed. Similarly, K:Mo is about 0.58and does not vary across the bed.

Sulfur content declines from the top to bottom of the bed while carboncontent increases. Acid-leachable cobalt is relatively low and roughlyconstant throughout the bed. Hydrogen content is comparable in themiddle and bottom of the bed and somewhat lower in concentration at thetop. One can assume that hydrogen occurs as CH₂ and that excess carbonis associated with Co or Mo.

S/M_(tot) Excess C/M_(tot) Acid leachable cobalt Fresh 1.98 ± 0.05 <00.088 ± 0.005 Top 1.52 ± 0.02 0.06 ± 0.06 0.24 ± 0.02 Middle 1.16 ± 0.020.30 ± 0.02 0.30 ± 0.08 Bottom 1.00 ± 0.01 0.48 ± 0.05 0.22 ± 0.02

For the middle and bottom of the bed, there is insufficient sulfur forMo to occur only as MoS₂. The excess carbon content suggests that metalcarbides may occur.

The leachability of cobalt evolves with time on stream in analcohol-synthesis reactor. In good Co/Mo/S powders, the fraction ofleachable cobalt is small, presumably since Co occurs as CoS₂ which,presumably, does not leach into 3 molar HCl at 93° C. After short tomoderate times (50-200 hr) on stream, the fraction of leachable cobaltrises to 30-50%. For longer times on stream the fraction of leachablecobalt decreases. Variable-temperature XRD experiments under syngasatmosphere reveal that crystalline CoS₂ rapidly reduces to crystallineCo₉S₈. It is expected that non-crystalline CoS₂ similarly reduces to CoSmaterials.

Assuming that leachable cobalt occurs as CoS, the amount of sulfuravailable to Mo can be determined. Assuming that sulfur combines with Moto make MoS₂, and given leachable Co as CoS, there is sufficient sulfurfor all the Mo at the top of the bed to occur as MoS₂, for 80% of themid-bed and 70% of the bottom-bed Mo to occur as MoS₂. It follows thatroughly 80% of the cobalt and up to 30% of the molybdenum do not occuras sulfides. The mole ratio of excess carbon to metal not occurring as asulfide is up to 0.5 at the top of the bed, 0.8 at mid bed, and about1.0 at the bottom of the bed. The majority of cobalt appears to occur ascobalt carbides throughout the bed while there is a gradient of putativemolybdenum carbides from the top to the bottom of the bed. The presenceof crystalline Co₂C was confirmed by XRD analysis.

Example 6 Co/Mo/S Catalyst Deactivation in Absence of Sulfur Addition

After running in a pilot unit for over 4000 hrs in the substantialabsence of H₂S, an alkali-promoted Co/Mo/S catalyst is unloaded underinert conditions and loaded into a laboratory reactor where it issubjected to sulfur-free syngas at 310° C. and separately at 325° C. Itis observed at either temperature that catalyst activity declines, theselectivity to ethanol declines (by about 30-40%), and the selectivityto hydrocarbons increases.

Deactivation is associated with changes in composition and chemicalproperties. For example, the ratio of sulfur to total metals drops fromabout 2 in the fresh catalyst to about 1.3 in deactivated catalysts.Furthermore, a significant portion of detected carbon in the deactivatedcatalysts can be assigned to the cobalt and molybdenum present, as metalcarbides. For example, crystalline Co₂C is observed by XRD indeactivated catalysts.

Example 7 Bulk Chemical Properties of Co/Mo/S Catalysts in the Presenceof Methanol, with and without H₂S

Two catalyst samples each from Run A and Run B are analyzed for total S,Co, Mo, C, H, K, 3N HCl-leachable S, Co, Mo, and K, carbonate carbon,and elemental sulfur.

In Run A, the catalyst is exposed to methanol for 72 out of 185 hours onstream; H₂S is absent. In Run B, the catalyst is exposed to methanol for226 out of 403 hours on stream; H₂S is present (about 80 ppm). It ishypothesized that H₂S co-feed can stabilize catalyst performance in theface of high amounts of methanol injection; this is verified in Run B.It is also hypothesized that sulfur loss is less pronounced given H₂Sco-feed.

S/(Co+Mo) is substantially lower in Run A discharge compared to Run Bdischarge. The values are 1.735 (Run B) and 1.65 (Run A); theprobability that these values are equal is only 2.2%. Cobalt leachingresults further support the hypothesis that the cobalt function isdamaged first as the catalyst losses sulfur. Only 18.0% of cobaltleaches into 3N HCl from Run B while 31.5% leaches from Run A. Theprobability that these values are equal is 1.6%. Molybdenum leachability(1.6% in Run B discharge, 1.4% in Run A discharge) is similar.

Assuming that Mo occurs as MoS₂, the transition-metal sulfidecompositions of the discharges are: 2MoS₂.CoS_(1.19) after Run B and2MoS₂.CoS_(0.95) after Run A. The higher level of S/Co after Run B isconsistent with persulfide playing a role in ethanol synthesis; about20% of cobalt could be associated with S₂ ²⁻.

Given the relatively highly sulfided nature of these compositions, it isunlikely that much transition-metal carbide occurs in these dischargematerials. A substantially larger fraction of carbon occurs as carbonatein Run B discharge. About 18.4% of carbon in Run B discharge occurs ascarbonate while in Run A, only about 12.3% of carbon occurs ascarbonate. The probability that these values are equal is 2.3%.

These results from bulk chemical analysis support the contention that acapable sulfide reagent maintains sufficient sulfur inventory in thecatalyst to enable relatively efficient ethanol synthesis. The fact thatcobalt leachability increases while molybdenum does not in the absenceof a sulfiding agent supports a hypothesis that the cobalt function isessential for ethanol formation. An interesting, unexpected differencebetween the two discharge samples is the higher fraction of carbon thatoccurs as carbonate carbon in the presence of a sulfiding agent.

Example 8 Accelerated Aging of a Sulfided Catalyst

A potassium-promoted Co—Mo—S catalyst with initial S/(Co+Mo)=2 isoperated under 2:1 CO:H₂ at 325° C. for several hundred hours. Duringthe first hundred hours, sulfur evolves from the catalyst due, in part,to reduction of some CoS₂ to CoS-type phases, such as Co₉S₈. After about100 hours, the amount of sulfur present in condensed alcoholic productis about 20 μg/ml.

After about 400 hours on stream, methanol together with 2:1 H₂:CO syngasis admitted to the top of the reactor. The methanol and syngas mixtureapproach to methanol synthesis equilibrium is between 25% and 50% at thetop of the reactor. The amount of sulfur present in condensed alcoholicproduct rises to about 160 μg/ml. The acceleration factor during thisperiod of methanol injection is about 8.

In this detailed description, reference has been made to multipleembodiments of the invention and non-limiting examples relating to howthe invention can be understood and practiced. Other embodiments that donot provide all of the features and advantages set forth herein may beutilized, without departing from the spirit and scope of the presentinvention. This invention incorporates routine experimentation andoptimization of the methods and systems described herein. Suchmodifications and variations are considered to be within the scope ofthe invention defined by the appended claims.

All publications, patents, and patent applications cited in thisspecification are herein incorporated by reference in their entirety asif each publication, patent, or patent application were specifically andindividually put forth herein. Also, this application herebyincorporates by reference herein U.S. patent application Ser. No.12/204,543, filed Sep. 4, 2008, whose assignee is the same as theassignee of this patent application.

Where methods and steps described above indicate certain eventsoccurring in certain order, those of ordinary skill in the art willrecognize that the ordering of certain steps may be modified and thatsuch modifications are in accordance with the variations of theinvention. Additionally, the steps may be performed concurrently in aparallel process when possible, as well as performed sequentially.

Therefore, to the extent there are variations of the invention, whichare within the spirit of the disclosure or equivalent to the inventionsfound in the appended claims, it is the intent that this patent willcover those variations as well. The present invention shall only belimited by what is claimed.

What is claimed is:
 1. A method of producing at least one C₁-C₄ alcoholfrom syngas, the method comprising: (a) providing a reactor including acatalyst composition comprising cobalt, molybdenum, and sulfur, whereinat least some of said cobalt and some of said sulfur are present as acobalt-sulfur association having a molar ratio of sulfur to cobalt(S:Co), calculated by assuming all molybdenum is present as MoS₂; (b)flowing syngas into said reactor at conditions effective to produce atleast one C₁-C₄ alcohol; and (c) injecting additional sulfur, or acompound containing sulfur, into said reactor, in an amount that issufficient to maintain at least some of said cobalt in a sulfided state,and is further sufficient to maintain said molybdenum in a completelysulfided state wherein said additional sulfur injected in step (c) iscontained in one or more compounds selected from the group consisting ofelemental sulfur, hydrogen sulfide, dimethyl sulfide, diethyl sulfide,dimethyl disulfide, dibutyl polysulfide, dioctyl polysulfide, diphenylpolysulfide, dicyclohexyl polysulfide, methylthiol, ethylthiol,cysteine, cystine, methionine, potassium disulfide, cesium disulfide,sodium disulfide, and any isomers thereof.
 2. The method of claim 1,wherein said molar ratio S:Co is controlled to between about 0.1 andabout
 4. 3. The method of claim 2, wherein said molar ratio S:Co iscontrolled to a ratio of at least
 1. 4. A method for maintainingcatalyst stability while producing at least one C₁-C₄ alcohol fromsyngas, said method comprising: (a) providing a reactor including acatalyst composition comprising cobalt, molybdenum, and sulfur; (b)flowing syngas into said reactor at conditions effective to produce atleast one C₁-C₄ alcohol; and (c) injecting additional sulfur, or acompound containing sulfur, into said reactor, in an amount that issufficient to inhibit the formation of cobalt carbides or molybdenumcarbides under said conditions effective to produce at least one C₁-C₄alcohol.
 5. The method of claim 4, wherein said step (c) inhibits theformation of cobalt carbides.
 6. The method of claim 5, wherein saidcobalt carbides include crystalline Co₂C.
 7. The method of claim 4,wherein said step (c) inhibits the formation of molybdenum carbides. 8.The method of claim 4, wherein said step (c) prevents the formation ofcobalt carbides or molybdenum carbides.
 9. The method of claim 4,wherein said additional sulfur maintains at least some of said cobalt ina sulfided state.
 10. The method of claim 9, wherein said additionalsulfur maintains said cobalt in a sulfided state.
 11. The method ofclaim 4, wherein said additional sulfur maintains said molybdenum in asulfided state.
 12. The method of claim 4, wherein said additionalsulfur injected in step (c) is contained in one or more compoundsselected from the group consisting of elemental sulfur, hydrogensulfide, dimethyl sulfide, diethyl sulfide, dimethyl disulfide, dibutylpolysulfide, dioctyl polysulfide, diphenyl polysulfide, dicyclohexylpolysulfide, methylthiol, ethylthiol, cysteine, cystine, methionine,potassium disulfide, cesium disulfide, sodium disulfide, and any isomersthereof.
 13. The method of claim 4, comprising maintaining, for at least1000 hours on-stream, one or more parameters selected from the groupconsisting of CO conversion, ethanol selectivity, total alcoholselectivity, total alcohol productivity, and methane selectivity. 14.The method of claim 4, further comprising recovering sulfur downstreamof said reactor and recycling at least a portion of said sulfur intosaid reactor.